This invention relates to password processing of processing passwords for a utilization device which is typically receiver circuitry of a selectively called portable radio receiver. The utilization device may be a cash dispenser connected to a bank on-line system. In this case, the password is what is usually called an identification number. More particularly, this invention relates to a password processing method and to a password processing device.
In a password processing device, a memory unit is preliminarily loaded with a unique password. Only when supplied with a correct password which correctly and exactly represents the unique password, a comparator puts the utilization device into operation. The password processing device rejects a foreign password which does not represent the unique password. In other words, attempts result in failure in putting the utilization device into operation when tried by one who is not authorized to use the utilization device.
A password processing device of the type described is disclosed in Japanese Patent Prepublication (A) No. 191,364 of 1985 by Mori-Ryoiti (transliteration in accordance with ISO 3602). In this Mori device, operation of the password processing device is suspended during a predetermined duration of time if an input password is the foreign one. The predetermined duration is, for example, twenty-four hours long. The Mori device is excellently operable to protect the utilization device against an illegal use by a hacker. The Mori device is, however, defective in that the hacker can put the utilization device into operation when attempts are repeated after lapse of each predetermined duration to tamper with the unique password.
Apparently independently improved password processing device and method are revealed by Thomas F. Holmes and two others in U.S. Pat. No. 5,073,767. This Holmes et al device is built in the utilization device and is disabled by an illegal use. The utilization device must therefore be returned to its manufacture for repair. Alternatively, the utilization device is inoperative unless its expensive components are replaced. More specifically, the password processing device is disabled or locked when supply thereto of guessed passwords fails a predetermined number of attempts. For example, the password processing device is locked out after seven times of failed attempts. Entire disabling of the utilization device is, however, objectionable depending on the circumstances. Incidentally, a programmable memory is used by Holmes et al to serve as the memory unit for storing the unique password and an encryption algorithm. It is described by Holmes et al to the effect that a subsequently entered correct password would functionally reenable the utilization device. Its details are, however, not clear.